It is well known in the current art to build spatial light modulators (SLM) of a micro mirror type U.S. Pat. Nos. 4,566,935, 4,710,732, 4,956,619. In general two main principles for building integrated devices, such as micro mirror SLM, have been employed.
An integrated circuit (IC) is manufactured to a finished state, and then the micro mirrors are manufactured on said IC. The micro mirrors are built onto the IC wafers. An advantage with this approach is that so called IC foundries can be used, which presents a very cost efficient manufacturing of the electronics wafers. A disadvantage is that there is a very restricted selection of materials and methods that are usable for the manufacturing of the micro mirrors, because there is an upper temperature limit of about 400° C., above which the electronics will be damaged. This makes the manufacturing of micro mirror having optimal performance more difficult.
Another way of building micro mirror SLM's is at the end of the process for making the IC, micro mirror manufacture may be started on the same wafers. An advantage with this approach may be that there is a greater freedom of selecting materials, methods and temperatures for the manufacture of micro mirrors having good performance. A disadvantage is that the IC wafers cannot be manufactured in standard IC foundries, because they have very strict demands on a process of manufacturing to be standardized in order to be able to maintain the quality in the process.
Yet another way of building micro mirror SLM's may be to manufacture the IC on a first wafer and a micromirror array on a second wafer. Said first and second wafers may be attached to each other by means of bonding. One problem with such a method may be the tight demands on the alignment between said first and second wafers, a misalignment may affect the functionality of one or several pixels.
Micromirrors in SLM may be made of aluminum due to its good optical performance. However, there may be some drawbacks by using mirrors made of Aluminum such as: the mirrors may not be perfectly flat, a mirror height may differ between mirrors, the mirrors may bend when tilted, the mirrors may sag when tilted, the mirrors may have a built in predeflection which may be different from mirror to mirror, the hinge may have anelastic behaviour.
Therefore, there is a need in the art for an improved method for manufacturing micro electrical/mechanical/optical integrated devices.